This invention relates to a phasing element and a variable electric depointing antenna comprising at least one such element.
In radiofrequency communications systems, of the mobile telephony type, the propagation of the signal representative of a user's voice goes through the antenna of the mobile telephone towards a base station. This signal is then routed via a wire network, for instance, towards another base station, which transmits the signal to the called party. Each base station, also called relay antenna, covers a portion of territory denominated “cell”. A service area is therefore composed of a set of cells forming a mesh network of base station.
In these networks, one may attempt to limit the radio range of an antenna by depointing its maximum radiation pattern downwards not to interfere with the adjacent cells. This depointing of the maximum radiation pattern is obtained by adjusting in a known fashion the relative amplitudes and the relative phases between the electric signals feeding each radiating element of an antenna, which comprises at least two radiating elements superimposed vertically on top of one another. The values imposed at these amplitudes and phases enable advantageously to impose the direction of the maximum radiation pattern, to mitigate unwanted secondary lobes and to fill in radiation holes in certain directions.
The embodiment of such antennas with adjustable beam tilt has been the subject matter of numerous breakthroughs these last few years. However, the adjustment of the relative phases of the electric signals is obtained by implementing big and costly mechanical elements. These elements include, for instance, sliding portions in the form of a circular arc, connected to electric power supply cables, the rotation of one of the portions enabling to vary the phase of the electric signal. These mechanical elements increase the weight of the base stations. Moreover, the volume of these elements impose generally to arrange them also on the face of the support receiving the radiating elements, whereas this face cannot then be totally metallized, or then impose to increase the thickness of the antenna to house these elements behind this face receiving the radiating elements.
Moreover, the antennas cellular network base station operate today very often on double polarisation, generally ±45°. In such a case, the source portion including the radiating elements is either doubled, with at least two radiating elements for each polarisation, or it includes radiating elements which operate themselves on double polarisation. In the former case, each radiating element has two accesses, one by polarisation.
In these double polarisation antennas, the lobe formation circuit which includes radioelectric circuits intended to distribute the energy between the feed point of the antenna and the different radiating elements so that the stacked array of these elements forms the radiation lobe requested, is doubled to maintain the isolation between the signals of each polarisation.
In the variable electric depointing versions of these double polarisation antennas, it is necessary to seek to obtain the same depointing value for the radiation lobes corresponding to each of both polarisations. It is therefore advisable to adjust simultaneously the phase adjustment means proper to each of both lobe formation circuits.
The object of this invention is to suggest a phasing element and an electrically variable beam tilt antenna simple in their design and in their operating mode, cheap and enabling an “all printed circuit” embodiment of the antenna, i.e. the lobe formation circuit is made of supply lines and of dividers engraved on such a printed circuit.
These phasing elements also enable by particularly compact arrangement to regroup on the same face of the printed circuit simultaneously the phasing elements and the power supply circuits of the elementary sources, even in the case of a double polarisation antenna, which enables to keep the other face of the printed circuit entirely metallized. It is the most favourable situation to provide therein the source portion comprising the radiating elements. This arrangement of the phasing elements promotes the association of a phasing element using a radiating element, which facilitates the control of the radiation pattern and of its important parameters (level of secondary lobes, filling in holes in the radiation pattern, pointing accuracy of the maximum radiation pattern).
Another object of the invention is to operate simultaneously all the phasing elements by dint of a single control while adhering to the law of relative phase variation relative between the elementary antennas. This single control also enables easy adjustment of the beam tilt angle. This adjustment may then be adjusted either manually at the antenna properly speaking, or in a motorised fashion by incorporating an engine at the antenna and by adjoining thereto position measuring means. In the case of motorised adjustment, the motorisation driving signals may come from either a piece of equipment installed at the base station fitted with the antenna, or with a remote management centre using one of the numerous existing telecommunications means to transmit the information necessary to driving the motorisation system.
To this end, the invention relates to a phasing element intended for inserting a variable lag in the transmission of an electric signal by variation of the electric path travelled by said signal in the phasing element.